Low-temperature specific heat in high-Tc cuprate Bi2Sr2−xLaxCuO6+δ (x ∼ 0.4): Probing the d-wave superconducting gap

Abstract

We present our recent low-temperature specific heat experiment on a nearly optimally doped Bi2Sr2−xLaxCuO6+δ (La-Bi2201) (x ∼ 0.4) single crystal. By studying the electronic specific heat owing to nodal quasiparticle excitations, the amplitude of the d-wave superconducting gap at the antinodes is determined to be Δo ∼ 12 meV It also enables us to estimate the coefficient of the normal-state electronic specific heat (Sommerfeld constant) of the sample to be γn ∼ 9 mJmol−1K−2. The quantitative probe of the superconducting gap mimics our previous findings in La2−xSrxCuO4 (LSCO) where the superconducting gap has been determined via specific heat as well but in a wide range of doping. By looking back the data in LSCO, it is shown that there seems to be a critical change in the doping dependence of the superconducting gap at about p ∼ 0.19. We discuss this anomalous behavior and suggest this be further checked in future specific heat measurement on La-Bi2201 or other cuprates at various doping levels.